The present disclosure relates to transmission, and more particularly to Semi-Continuous Variable Transmission (sCVT), and infinitely variable transmission (IVT).
Although CVTs and IVTs were typically used in the automotive field, their torque capabilities and reliability have been limited in the past. Conventional transmissions allow for the selection of discrete gear ratios, thus limiting the engine to providing maximum power or efficiency for limited ranges of output speed.
There are several classifications of CVTs; hydrostatic, friction and traction. Friction CVT is one of the most common forms of CVTs in use. These CVTs are based on friction between two or more rotating components to transmit power between a motor and a wheel axle, the radius for the point of contact can be varied, this typically archived with a variable-diameter pulley (VDP). Friction/traction CVT has proven problematic to certain applications due to large size (weight), high cost of components, material fatigue resulting in performance lost and other issues.
Alternatively, Toroid Traction-Drive transmissions use the high shear strength of viscous fluids to transmit torque between an input torus and an output torus. In properly designed traction drives, power is transferred from the driving roller to the driven roller through the shearing of the fluid film between the toroids (conical portions) and the rollers. Toroid Traction-Drive transmissions has proven problematic to certain applications due to transient elastohydrodynamic lubrication problems, size (weight), overheating of pads, loss of friction and other issues.
Likewise, Hydrostatic (HST) CVT is typically based on hydraulic pump coupled to a hydraulic motor, where, by varying the displacement per revolution of pump and motor, the transmission ratio will define the torque and speed typically controlled by external means. HST though, has proven problematic to certain applications due to low efficiency of transmission, limited speed range and narrow shift range. Low speed high efficiency, high speed low efficiency.
CVTs/IVTs are currently being developed in conjunction with hybrid electric vehicles. As CVT/IVT development continues, costs may be further reduced and performance will improve, which in turn makes further development and application of CVT/IVT technology desirable.